Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures

440.3R-04 Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete StructuresTarek Alkhrdaji Edward R. Fyfe Vistasp M. Karbhari Morris Schupack
Charles E. Bakis Ali Ganjehlou James G. Korff David W. Scott
P. N. Balaguru Duane J. Gee Michael W. Lee Rajan Sen
Lawrence C. Bank T. Russell Gentry† John Levar Mohsen A. Shahawy
Abdeldjelil Belarbi Janos Gergely Ibrahim Mahfouz Carol K. Shield
Brahim Benmokrane* William J. Gold Henry N. Marsh Khaled A. Soudki
Gregg J. Blaszak Nabil F. Grace Orange S. Marshall Robert E. Steffen
Timothy E. Bradberry Mark F. Green Amir Mirmiran Gamil Tadros
Gordon L. Brown Mark Greenwood Ayman S. Mossallam Jay Thomas
Vicki L. Brown Doug D. Gremel Antonio Nanni Houssam A. Toutanji
Thomas I. Campbell H. R. Hamilton Kenneth Neale Miroslav Vadovic
Charles W. Dolan Issam E. Harik John P. Newhook David Vanderpool
Dat Duthinh Kent A. Harries Max L. Porter Milan Vatovec
Garth J. Fallis Mark P. Henderson Mark A. Postma David White
Amir Fam Bohdan N. Horeczko Hayder A. Rasheed
Sami H. Rizkalla Chair
John P. Busel Secretary
Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures
Reported by ACI Committee 440
ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.
Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.
It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. ACI does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards.
Fiber-reinforced polymer (FRP) materials have emerged as a practical material for producing reinforcing bars and laminates for concrete struc- tures. FRP reinforcing bars and laminates offer advantages over steel rein- forcement in that FRP is noncorrosive and nonconductive. FRP reinforcing
440.3
ACI 440.3R-04 became effective June 28, 2004. Copyright © 2004, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any
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bars, grids, and tendons are being used for nonprestressed and prestressed concrete structures. FRP laminates are being used as external reinforcement for strengthening of existing concrete and masonry structures. Due to differ- ences in the physical and mechanical behavior of FRP materials compared to steel, unique test methods for FRP bars and laminates are required.
This document provides model test methods for the short-term and long- term mechanical, thermo-mechanical, and durability testing of FRP bars and laminates. It is anticipated that these model test methods may be considered, modified, and adopted, either in whole or in part, by a U.S. national standards-writing agency such as ASTM International or AASHTO. The publication of these test methods by ACI Committee 440 is an effort to aid in this adoption.
The recommended test methods are based on the knowledge gained from research results and literature worldwide. Many of the proposed test methods for reinforcing rods are based on those found in “Recommendation for Design and Construction of Concrete Structures using Continuous Fiber Reinforcing Materials” published in 1997 by the Japan Society for Civil Engineers (JSCE). The JSCE test methods have been modified extensively to add details and to adapt the test methods to U.S. practice.
Keywords: anchorage; bond; concrete; coupler; creep; fatigue; fiber- reinforced polymers (FRP); modulus of elasticity; reinforced concrete; shear; splice; stirrup; strength; tendon.
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CONTENTS Part 1—General, p. 440.3R-2
1.1—Introduction 1.2—Scope 1.3—Existing ASTM test methods 1.4—Definitions 1.5—Notation
Part 2—Test methods for FRP bars for concrete structures, p. 440.3R-7
B.1—Test method for cross-sectional properties of FRP bars B.2—Test method for longitudinal tensile properties of
FRP bars B.3—Test method for bond strength of FRP bars by
pullout testing B.4—Test method for transverse shear strength of FRP bars B.5—Test method for strength of FRP bent bars and
stirrups at bend locations B.6—Accelerated test method for alkali resistance of FRP
bars B.7—Test method for tensile fatigue of FRP bars B.8—Test method for creep rupture of FRP bars B.9—Test method for long-term relaxation of FRP bars B.10—Test method for performance of anchorages of
FRP bars B.11—Test method for tensile properties of deflected FRP bars B.12—Test method for determining the effect of corner
radius on tensile strength of FRP bars
Part 3—Test methods for FRP laminates for concrete and masonry, p. 440.3R-30
L.1—Test method for direct tension pull-off test L.2—Test method for tension test of flat specimen L.3—Test method for overlap splice tension test
References, p. 440.3R-36 R.1—Guides and related standards R.2—Conference proceedings R.3—Individual papers, reports, and theses
Appendix A—Anchor for testing FRP bars under monotonic, sustained, and cyclic tension, p. 440.3R-38
Appendix B—Methods for calculating tensile properties of flat specimen, p. 440.3R-39
PART 1—GENERAL 1.1—Introduction
Conventional concrete structures are reinforced with nonprestressed steel, prestressed steel, or both. Recently, composite materials made of fibers embedded in a polymeric resin, also known as fiber-reinforced polymers (FRPs), have become alternatives to steel reinforcement for concrete structures. Because FRP materials are nonmetallic and noncorrosive, the problems of steel corrosion are avoided with FRP reinforcement. Additionally, FRP materials exhibit several properties, such as high tensile strength, that make them suitable for use as structural reinforcement. FRP materials are supplied as bars for reinforced and prestressing applications and in flat sheets or laminates for use as repair materials for concrete structures.
The mechanical behavior of FRP differs from the behavior of steel reinforcement. FRP materials are anisotropic due to the fiber orientation in the bars and laminates and are characterized by high tensile strength only in the direction of the reinforcing fibers. This anisotropic behavior affects the shear strength and dowel action of FRP bars and the bond performance of FRP bars to concrete.
FRPs are available with a wide range of mechanical properties (tensile strengths, bond strengths, and elastic moduli). Generally, FRP concrete reinforcements are not covered by national material standards, as few such stan- dards exist. Instead, manufacturers of FRP provide test data and recommend design values based on these test data. Unfortunately, also due to the lack of material standards, few standard test methods exist for FRP concrete reinforcements. Therefore, it is difficult to compare test results between product manufacturers. In addition, research has considered the durability of FRP concrete reinforcements in environ- ments containing moisture, high and low temperatures, and alkaline environments. Test methods that allow for the comparison of mechanical property retention in a wide range of standard environments are needed so that durable FRP- reinforced concrete structures can be ensured.
1.2—Scope This document provides model test methods for deter-
mining the short-term and long-term mechanical properties of FRP reinforcing bars, grids, and tendons for concrete, both prestressed and nonprestressed, and for FRP laminates as external reinforcement for concrete structures. As noted in the individual methods, most of the methods for bars are also suitable for tendons and sections cut from grids. Where necessary, the tests consider the bars and laminates acting in concert with concrete. For the most part, however, these tests are considered to be material tests and not component or structural tests.
These model test methods are intended to be considered, modified, and adopted, either in whole or in part, by a U.S. national standards-writing agency such as ASTM Interna- tional or AASHTO. The publication of these test methods by ACI Committee 440 is an effort to aid in this adoption.
The document contains only test methods and not material standards. The individual test methods contained in this document do not specify minimum material properties that must be met for the materials to be considered acceptable for use. Guidance on deciding whether a material is acceptable based on test results is made in the material specifications and design provisions that complement these test methods (ACI 440.1R; ACI 440.2R).
The test methods presented in this document are the recommendations of ACI Committee 440, and have not been adopted by ACI as standards. As such, they are, for the most part, written in nonmandatory language, using “should” and “may” rather than “shall” and “must.” In keeping with the usual test method format, however, some language is imper- ative (“Fill a cylinder with water...” rather than “A cylinder should be filled with water...”). Although typically considered to be mandatory language, the use of imperative language in
GUIDE TEST METHODS FOR FIBER-REINFORCED POLYMERS 440.3R-3
these test methods is for readability, and remain as committee recommendations only. If an architect or engineer desires one of the test methods to be part of the contract documents, all of the nonmandatory language would need to be restated into mandatory language.
1.3—Existing ASTM test methods The recommended test methods provided herein are based
on the knowledge obtained from research results and literature worldwide. Relevant ASTM standards are referenced in the individual methods; others are listed in Table 1.1. In many
cases, existing ASTM test methods are appropriate to deter- mine material properties for FRP bars and laminates. Where such methods are completely acceptable for FRP reinforce- ments, no new method has been proposed. The new methods that are provided have been developed for one or more of the following reasons:
1. To provide a test method where no current method exists; 2. To provide more detailed requirements that are specific
to FRP concrete reinforcing bars or laminates, such as details on how to grip the reinforcements in the test fixture;
3. To adapt a test method originally developed for steel reinforcing bars to work with FRP bars; or
4. To provide calculated test results that are compatible with other ACI documents.
Table 1.1 lists specific ASTM test methods and comple- mentary ACI 440 methods for various material properties. Where both ASTM and ACI 440 test methods exist, the differences between the methods are summarized. Hundreds of ASTM test methods are applicable to FRP composites and organic polymers. The table only describes key material properties and selected ASTM tests that can be used to deter- mine these properties. For some properties, ASTM provides more than one test procedure. The table does not attempt to discuss the differences between various ASTM test methods.
1.4—Definitions The following definitions clarify terms that are not
commonly used in reinforced concrete practice.
-A- AFRP—aramid fiber-reinforced polymer. aging—the process of exposing materials to an environ-
ment for an interval of time. alkaline—having a pH greater than 7 (OH– concentration
greater than 1 × 10–7 M). anchorage—a device at the ends of an FRP bar that grips
the bar, allowing a minimum of slip and transfers prestressing load from the tendon to the concrete members.
anchorage reinforcement—the latticed or spiral reinforcing steel or FRP bars as confining reinforcement connected with the anchorage and arranged behind it.
anchoring section—the FRP bar section embedded in the anchorage and anchorage reinforcement, including the surrounding concrete.
average load (stress)—the mean value of the maximum and minimum repeated loads (stresses).
-B- bar, FRP—a composite material formed into a long,
slender, structural shape suitable for the internal reinforcement of concrete and consisting of primarily longitudinal unidirec- tional fibers bound and shaped by a rigid polymer resin material. The bar may have a cross section of variable shape (commonly circular or rectangular) and may have a deformed or roughened surface to enhance bonding with concrete.
bending angle—the angle formed by the straight sections of a specimen on either side of the deflector.
bending diameter ratio—the ratio of the external diameter of the deflector surface in contact with the FRP bar to the diameter of the FRP bar.
bending tensile capacity—the tensile capacity at failure of a specimen within the deflected section.
bonded length—the length of the test bar that is in contact with concrete.
braiding—intertwining fibers in an organized fashion.
-C- CFRP—carbon fiber-reinforced polymer.
characteristic length—for bars or tendons that have a repeating surface deformation pattern, the characteristic length is the distance (in mm) of this pattern. For a spiral pattern, the characteristic length is the pitch.
coefficient of thermal expansion (CTE)—a measure of the relative change in linear dimension in a material based on a unit increase in temperature of that material. Note: Due to the anisotropy of FRPs, the CTE in the longitudinal direction of the rod is likely to be different from that measured in the transverse direction.
composite—a combination of one or more materials differing in form or composition on a macroscale. Note: The constituents retain their identities; that is, they do not dissolve or merge completely into one another, although they act in concert. Normally, the components can be physi- cally identified and exhibit an interface between one another.
creep—time-dependent deformation (or strain) under sustained load (or stress).
creep rupture—material failure due to deformation (accumulated strain) caused by creep.
creep rupture capacity—the load at which failure occurs after a specified period of time from initiation of a sustained load.
creep rupture strength—the stress causing failure after a specified period of time from initiation of a sustained load.
creep rupture time—the lapsed time between the start of a sustained load and failure of the test specimen.
creep strain—the differential change in length per unit length occurring in a specimen due to creep.
cure—to irreversibly change the properties of a thermo- setting resin by chemical reaction such as condensation, ring closure, or addition. Note: Cure can be accomplished by adding curing (cross-linking) agents with or without heat and pressure.
440.3R-4 ACI COMMITTEE REPORT
Table 1.1—Test methods for bars used for reinforcing or prestressing concrete
Property ASTM test method(s)
Cross-sectional area — B.1 No existing ASTM test method available.
Longitudinal tensile strength and modulus D 3916 B.2
ACI method provides detailed information on anchoring bars in the test fixture. ACI method also provides procedural requirements for attachment of elongation reading devices on bar with various deformation patterns.
Bond properties A 944 B.3
ASTM Pullout Test C 234 has been withdrawn and, as written, did not provide adequate specimen size to prevent splitting of concrete cylinder when using FRP bars. The only remaining ASTM test method for bond of steel bars to concrete is beam-end test method (A 944), which has not been modified for use with FRP bars. Ongoing work by ACI Committee 440 is expected to produce beam bond test methods.
Shear strength
D 5379
B.4 The ACI method focuses on dowel action of bars and does not overlap with existing ASTM methods that focus mainly on beam shearing failure modes. Bar shear strength is of specific concern for applications where FRP rods are used to cross construction joints in concrete pavements.
D 3846
D 2344
D 4475
Bent bar capacity — B.5 No existing ASTM test methods available.
Durability properties — B.6 No existing ASTM test method available.
Fatigue properties D 3479 B.7 ACI methods provide specific information on anchoring bars in the test fixtures and on attaching elongation measuring devices to the bars. The ACI methods also require specific calculations that are not provided in the ASTM methods.
Creep properties D 2990 B.8
Relaxation properties D 2990
Anchorage properties — B.10 No existing ASTM test methods available.
Tensile properties of deflected bars — B.11 No existing ASTM test methods available.
Effect of corner radius on strength — B.12 No existing ASTM test method available.
Flexural properties D 790
Coefficient of thermal expansion
D 696
D 648
E 2092
Test methods for laminates used as strengthening and repair materials
Direct tension pulloff D 4551 L.1 ACI method provides specific requirements for specimen preparation not found in the ASTM test method.
Tensile strength and modulus D 3039 L.2 ACI method provides for calculating tensile strength and modulus on gross cross-sectional and equivalent, fiber area basis.
Lap shear strength D 3165
L.3 ACI method provides specific requirements for specimen preparation. D 3528
Bond strength D 4551
— No ACI methods developed. C 882
-D- deflected section—the section of an FRP bar that is bent
and maintained at the required bending angle and bending diameter ratio.
deflector—a device used to maintain the position, alter the bending angle, or alleviate the stress concentrations in the FRP bar. Such a device may sometimes be installed in the deflected section.
deformability—the ratio of energy absorption (area under the moment-curvature curve) at ultimate strength level to the energy absorption at service level.
degradation—a decline in the quality of the mechanical properties of a material.
development length—length of embedded reinforcement required to develop the tensile capacity.
-E- E-glass—a general-purpose fiber that is used in reinforced
polymers; a family of glass with a calcium, alumina, and boro- silicate composition and a maximum alkali content of 2%.
equivalent area—area determined according to Test Method B.1.
equivalent circumference—circumference of an assumed circle with the equivalent area determined according to Test Method B.1.
GUIDE TEST METHODS FOR FIBER-REINFORCED POLYMERS 440.3R-5
-F- fatigue life—the number of cycles of deformation or load
required to bring about failure of a material, test specimen, or structural member.
fatigue strength—the greatest stress that can be sustained for a given number of load cycles without failure.
fiber—any fine thread-like natural or synthetic object of mineral or organic origin. Note: This term is generally used for materials whose length is at least 100 times its diameter.
fiber, aramid—highly oriented organic fiber derived from polyamide incorporating into an aromatic ring structure.
fiber, carbon—fiber produced by heating organic precursor materials containing a substantial amount of carbon, such as rayon, polyacrylonitrile (PAN), or pitch, in an inert environment.
fiber, glass—fiber drawn from an inorganic fusion of silica (SiO2) and other compounds that has cooled without crystallization.
fiber content—the amount of fiber present in a composite. Note: This is usually expressed as a percentage volume fraction or weight fraction of the composite. Due to differing constituent densities, weight fractions and volume fractions of fibers are not the same.
fiber-reinforced polymer (FRP)—composite material consisting of continuous fibers impregnated with a fiber- binding polymer then molded and hardened in the intended shape.
fiber-volume fraction—the ratio of the volume of fibers to the volume of the composite.
fiber-weight fraction—the ratio of the weight of fibers to the weight of the composite.
frequency—the number of loading (stressing) cycles per second.
-G- gauge length—the distance between two gauge points
on the test section, over which the percentage of elongation is determined.
GFRP—glass fiber-reinforced polymer. glass-transition temperature Tg—the midpoint of the
temperature range over which an amorphous material changes from (or to) a brittle, vitreous state to (or from) a plastic state.
grid—a two-dimensional (planar) or three-dimensional (spatial) rigid array of interconnected FRP bars that form a contiguous lattice that can be used to reinforce concrete. Note: The lattice can be manufactured with integrally connected bars or made of mechanically connected individual bars.
-H- hybrid—an FRP that is reinforced with a combination of
two or more different…